The present invention relates to a reinforced polypropylene composition and more particularly to a reinforced polypropylene composition comprising inorganic fillers, which is suitable for the production of molded articles having high rigidity, high heat resistance and excellent resistance to warpage deformation.
It has hitherto been conducted to incorporate into a polypropylene various fillers such as fibrous fillers, e.g. glass fiber, carbon fiber, whiskers and metal fibers, plate-like fillers, e.g. mica, talc, kaolinite and glass flakes, and granular fillers, e.g. calcium carbonate, diatomaceous earth, alumina and glass beads, to obtain a polypropylene molded article with improved mechanical strength, rigidity, heat deformation resistance, etc. Such polypropylene molded articles are already in wide use in various applications.
Of the above fillers of various forms, the fibrous fillers, as compared with the fillers of other forms, have a very large reinforcing effect. Polypropylene compositions reinforced particularly with a glass fiber are a material which is suitable for producing a molded article of high rigidity and high heat resistance, and are in wide use in various fields. However, when a glass fiber-reinforced polypropylene composition is used to produce a large-sized molded article, the molded article is satisfactory in rigidity and heat resistance but gives large warpage deformation. This warpage poses a major problem when a glass fiber-reinforced polypropylene composition is used as a material for production of a large-sized molded article.
Meanwhile, when a plate-like filler or a granular filler is used, the resulting reinforced polypropylene composition gives reduced warpage deformation but shows a significantly lower effects in tensile strength, flexural strength and Izod impact strength than a polypropylene composition reinforced with a fibrous filler. Since a polypropylene composition reinforced with a plate-like filler such as mica or talc provides a molded article of good rigidity, there were made attempts to use a fibrous filler and a plate-like filler in combination [see, for example, Japanese Patent Application Kokai (Laid-Open) Nos. 52-36141, 54-130647, 55-16049, 55-21438, 55-45715, 58-206659, 59-226041, 60-23432, 61-98758, etc.]. However, even those reinforced polypropylene compositions disclosed in the above patent documents are unable to provide a molded article which is fully satisfactory in warpage and twist.